The primary means by which most neurons communicate with their target cells is through the regulated release of neurotransmitter from synapses. Modulation of the release properties of these synapses has long been postulated, and in certain instances been directly demonstrated, to be a critical component of the cellular mechanisms that underlie learning and memory. Although a large number of proteins which may play significant roles in the release process have been molecularly characterized, the mechanisms that coordinate calcium-mediated fusion of transmitter-filled vesicles at the presynaptic terminal remain poorly understood. The objective of this research proposal is to investigate the mechanisms that regulate this release process. The molecular characterization of components of the synaptic vesicle release machinery has revealed that many of these molecules are highly conserved in all metazoans, including the nematode C. elegans. We propose to use the molecular genetic tools available for the study of C. elegans to explore the role of synaptic proteins in regulating release by characterizing the synaptic defects in mutants lacking individual synaptic components. In our initial work, we have molecularly characterized genes encoding four C. elegans synaptic components and have characterized mutants perturbing the function of two of these, rab3 and synaptotagmin. Building upon this foundation, we propose to 1) isolate additional mutants lacking other synaptic components that have been implicated by biochemical studies to play roles in synaptic vesicle fusion, 2) to determine the significance of individual components in mediating vesicle fusion by characterizing the synaptic defects in these mutants and 3) to identify novel components acting in this release pathway by characterizing suppressors and enhancers of well characterized synaptic mutants. This molecular genetic method of examining synaptic function is complementary to the biochemical approaches other researchers are using to study this highly conserved process. Our goal is a complete description of the molecular mechanisms transmitter release from synaptic terminals.